This series of experiments seeks to determine the necessary and sufficient factors in the etiology of pica (the consumption of seemingly non-nutritive substances) and to validate the utility of pica as a behavioral assay of toxicosis. A variety of toxic substances have been shown to cause laboratory rats to engage in geophagia (earth eating). Moreover, rats poisoned with logarithmic doses of toxic substances consume amounts of non-nutritive substances proportionate to the amount of poison administered. Other factors demonstrated to be involved in the etiology of pica include gastrointestinal malaise and the acquisition of a conditioned illness. The objectives of this research are (1) to investigate the etiology of pica, (2) to evaluate pica as a behavioral assay of toxicosis in the rat, and (3) to assess the functional utility of pica during poison-induced illness.